Polymers derived from the ring opening polymerization of benzoxazines compete with phenolic, epoxy and other thermoset or thermoplastic resins in various applications, such as in prepregs, laminates, PWB's, molding compounds, sealants, sinter powders, cast articles, structural composites and electrical components. The benzoxazines, which are synthesized by reacting a phenol with an amine and an aldehyde in the presence or absence of a solvent, have been shown to be, upon curing, dimensionally stable with good electrical and mechanical resistance, low shrinkage, low water absorption, and having medium to high glass transition temperatures. One drawback to the use of benzoxazine resins is that they generally require higher curing temperatures in order to build up enough physical properties.
Benzoxazines are known to have been combined with various epoxy resins to produce curable compositions (see e.g., U.S. Pat. No. 4,607,091 (Schreiber), U.S. Pat. No. 5,021,484 (Schreiber), U.S. Pat. No. 5,200,452 (Schreiber) and U.S. Pat. No. 5,443,911 (Schreiber)). Because the epoxy resin reduces the melt viscosity of the benzoxazine, these blends have been shown to be useful in electrical applications since the blend is able to handle higher filler loadings yet still maintain a processable viscosity. One drawback to the use of such blends however is that higher curing temperatures are again usually necessary because of the addition of the epoxy. Furthermore, although these blends exhibit high glass transition temperatures after curing, toughness and stiffness are usually sacrificed to some degree.
More recently, blends of benzoxazines and a dianhydride have been tried (see C. Jubsilpa et al., “Property Enhancement of Polybenzoxazine Modified with Dianhydride”, Polymer Degradation and Stability, 96, 1047-1053 (2011)). These blends are solvent-based due to the high melting point and poor processability of the particular dianhydride used, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride. These blends are therefore less desirable due to the creation of voids caused by solvent escape, the environmental impact of vaporized solvent, and the redeposition of outgassed molecules on the surface of the cured article.
In U.S. Pat. No. 6,207,786, ternary blends of benzoxazines, epoxy resins, and phenolic resins are disclosed. However, it has been found that the addition of phenolic resins to the blend often lowers crosslink density during curing leading to cured articles having lower than desired glass transition temperatures.
Finally, in U.S. Pat. Pub. 20130266737, a composition containing a polymerization catalyst for curing benzoxazines is disclosed which includes the combination of a nitrogen-containing heterocycle and an organic sulfur-containing acid. However, it is known that use of strong acids in the polymerization of curable materials can negatively affect the physical properties of the cured material.
Notwithstanding the state of the technology, it is an object of the present disclosure to provide an improved benzoxazine-based composition which, upon low temperature cure, is able to perform thermally, mechanically and physically at high temperatures for long periods of time, therefore making it useful in high temperature applications within various industries, such as the aerospace, electronic and automotive industries.